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Old 20th January 2010, 11:45 PM   #981
Bill_P is offline Bill_P  United States
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The supplied caps are 10uF 50V
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Old 21st January 2010, 12:21 AM   #982
dasein is offline dasein  United States
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Opps nevermind then.
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Old 21st January 2010, 12:30 PM   #983
AndrewT is offline AndrewT  Scotland
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Originally Posted by dasein View Post
1) I live in the US and I'm trying to figure out how to safely ground the chassis and everything. I'm building a stereo with one rectifier and transformer. Can any more experienced DIYers in the US suggest what screw size and bolts and gauge wire I should be using to ground things to Safety Earth? Otherwise I was going to emulate P. Daniel's set up at the beginning of this thread to the best of my abilities.
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Originally Posted by Bill_P View Post
1. I use 14 gauge wire for safety ground crimped into a ring tongue terminal. The screw should be 8-32 or larger and a lockwasher should be used under the nut.
The Safety Earth has ONE wire going to it. Only 1.
That is the third wire in the mains power input cable.
Once this is permanently fixed to the chassis, nothing else disturbs this permanent fixing.

You can connect the Audio Ground above that permanent nut with two extra nuts. Or you can connect the Audio Ground to a separate point on the chassis.
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Old 21st January 2010, 02:13 PM   #984
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I shrunk the case dimensions.
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Old 29th January 2010, 01:55 PM   #985
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Default Hum, after some months

Hi,

I am a newbie who built two monoblocks based on the LM3875 AUDIOSECTOR premium kit following the instructions of this thread. They are now playing from about 6 months and I am very pleased of the sound.

Some weeks ago one of the monoblock started to produce a hum (low level noise) I could hear directly from the amps and also from the speakers. At first the hum was only occasional, for instance switching off for a couple of minutes was sufficient to cancel the hum when switched on again. But now the noise is becoming more and more frequent.

Have you any idea why? Is it possible a transformer failure?


Thank you

Renato
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Old 29th January 2010, 01:58 PM   #986
AndrewT is offline AndrewT  Scotland
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Hi,
find out if anything is running hot or shows signs of previous overheating.
Check output offset with and without the hum.
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Old 29th January 2010, 03:49 PM   #987
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Very interested after reading this thread in building 2 amplifiers. First would be a 4 channel LM4780 (to power midbass and sub), second would be a 4 channel LM3875 (to power mids and highs).

Do you have a kit for a 4 channel amp of each type or would it just require buying (2) of each kit? Also, can I use a single transformer in each of the two amplifier cases and which size would you recommend?

For reference, I live in the US with standard 120v mains, and the speaker loads will 4ohms.
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Old 29th January 2010, 04:06 PM   #988
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A single LM4780 kit can actually produce 4 separate amplification channels. It's only when you want to go parallel you need two of them.

As for LM3875, each kit is good for two channels. You can request a kit without PS section though.

I would recommend separate transformer per channel: 250-300VA would be a good size.

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Originally Posted by northernsky View Post
started to produce a hum (low level noise) I could hear directly from the amps and also from the speakers.
Good be a loose ground too.
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Old 29th January 2010, 04:19 PM   #989
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Quote:
Originally Posted by Peter Daniel View Post
A single LM4780 kit can actually produce 4 separate amplification channels. It's only when you want to go parallel you need two of them.

As for LM3875, each kit is good for two channels. You can request a kit without PS section though.

I would recommend separate transformer per channel: 250-300VA would be a good size.
Thanks for the quick response. So then (2) LM4780 kits would probably be ideal for me then I guess. Since there are 8 total amplification channels (as you said, 4 per kit), are you saying I would require 2 transformers, one for each LM4780 kit or am I misunderstanding you?

Thank you. Looking forward to getting an order in
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Old 29th January 2010, 06:37 PM   #990
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I guess so: you need 4 amps per channel and one transformer would be fine, per channel (preferably 300 - 400 VA)
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